1. Field of the Invention
The present invention relates to a power supply system and an electronic device comprising the power supply system, and more particularly relates to a power supply system which comprises a power generation section capable of generating power by use of a power generation fuel, which can be connected with an external power supply, and which can drive a load with electric power generated by the power generation section or electric power supplied from the external, and to an electronic device which comprises the power supply system and is driven by the power supply system.
2. Description of the Related Art
Recently, research and development have been keenly conducted for practical application and prevalence of fuel cells as a next-generation mainstream power supply system which have a significantly small impact on the environment (environmental burden) and a relatively high power generation efficiency (energy conversion efficiency) of about 30 to 40%, with a growing concern for environmental issues and energy problems.
Such a power generation system using the fuel cell is being put into practical use and commercialized, for example, in an automobile field, as a power supply unit for an electric automobile which applies an electric motor as a driving device instead of a gasoline engine or diesel engine with a heavy environmental burden due to emission of an exhaust gas and the like. As a technique for the fuel cell in a vehicle, such a configuration is known that comprises, for example, an energy battery constituted of a fuel cell which regularly generates constant electric power and a relatively large-sized power battery constituted of a secondary battery such as a lead battery, wherein switch control is carried out: motor driving electric power is supplied from the energy battery in an operating state with a light vehicle-driving load, while motor driving electric power is supplied from the power battery when the driving load is increased.
As described above, the power supply system using the fuel cell has conventionally been developed for application in the electric automobiles and the like which are relatively large-sized, operated continuously for relatively a long time, and are not frequently controlled to start and stop, and such a power supply system has a configuration provided with a relatively large battery for power holding. In such a configuration, the battery is fully charged, for example, through an external power supply such as a commercial alternating current power supply in an initial state of the power supply system (fuel cell) before started, and then the fuel cell is once started with the charged power, thus relatively easily enabling a constantly stable operating state under a usage condition where start/stop controls are not made frequently.
On the other hand, portable devices driven by batteries such as notebook-sized personal computers, digital cameras, personal digital assistances (PDA) and mobile telephones that have been significantly popular in recent years are required to cope with increasing power consumption due to more sophisticated functions, much longer operation time, and the like. One way considered to deal with these requirements is to make the power generation system using the fuel cell as described above smaller and lighter to install it as the power generation unit for those portable devices, and thus research and development for such a purpose are actively conducted. If the power generation system using the fuel cell is to be applied as the power generation unit for such portable devices, problems as indicated below are posed.
When the power generation system using the fuel cell is used for the portable devices and the like, it is difficult to mount a high-capacity large secondary battery and capacitor as batteries for power holding in terms of space and weight, so that a relatively small secondary battery and capacitor have to be used. Therefore, charging capacity of the secondary battery and capacitor becomes small in proportion to their volumes, areas and the like, which makes it difficult to ensure sufficient capacity. Moreover, for example, the portable devices such as the digital cameras and PDA are characterized by their usage in which start and stop operations are relatively frequently performed. Therefore, in a configuration in which charged power is utilized for starting the fuel cell, even if the battery is charged with sufficient electric power in the initial state, the electric power consumed to start the fuel cell might surpass the electric power generated by the fuel cell to supply and charge the battery because of the start and stop operations of the fuel cell that are frequently repeated, and in which case the charging power of the battery is gradually decreased. If the charging power of the battery has decreased below the minimum power required for starting, the fuel cell can not be started, which might cause inconvenience in using the portable devices. Further, if the start and stop operations of the fuel cell are frequently repeated as described above, fuel consumption efficiency of the fuel cell is also lowered because of the relatively large electric power consumed to start the fuel cell.